The use of various means to produce a flash during exposure of a photographic image, is well known. Currently, electronic flash units using xenon or the like, flash tubes, are typically used. While such electronic flash units are reliable and produce many flashes during their lifetime, they represent a substantial fixed cost component of the camera. For most cameras, this is not a problem since, compared to the rest of the camera components, the fixed cost of an electronic flash unit is relatively low and so does not influence the price of the camera much.
In recent years though, so called "single use cameras" (sometimes referred to as "film with lens" or similar terms) have become available. These cameras are sold to the end user with film pre-loaded in them, and are provided with an associated indication (usually in express written instructions on them) that the entire camera is to be returned to a processor for processing of the film. At the processor, the film is removed for processing but the camera is not returned to the user (often they are repaired as necessary and re-loaded with film for sale as a single use camera again). It is necessary in such camera to keep component cost as low as possible. In such single use cameras or other low cost cameras, the fixed cost of an electronic flash unit represents a substantial proportion of the overall camera cost which it would be desirable to reduce.
Combustion flash units which produce a flash by rapid combustion of a suitable material, were well known historically. Ignition of the combustible material was timed to occur close to the opening of a camera shutter to expose a photographic film. Many such devices used a percussion ignition source which would be ignited by a blow to the ignition source, and would in turn ignite the combustible material which produced the flash. An example of such a combustion flash is disclosed, for example, in GB 1,446,658. A difficulty with percussion ignitors is that a striker and some relatively complex activation mechanism for rapidly moving the striker, must be provided. While this may not normally appear to be an expensive proposition, in the context of single use cameras where costs must be minimized, costs of a striker and activation mechanism are a concern. Complex devices, in which openly exposed flash powder is ignited by a match, have been described in U.S. Pat. No. 684,499 and U.S. Pat. No. 1,330,149. However, such devices are clearly inappropriate for use with single-use cameras and also can release considerable noxious gasses and smoke during ignition.
It would be desirable then to provide a combustion flash unit, suitable for use with single-use cameras in particular, in which combustion can be initiated without the use of relatively mechanically complex percussion ignitor devices and which can allow little or no undesirable combustion gases to escape to the surrounding atmosphere.